Bone Marrow Transplantation (2018) 53:1599–1602 https://doi.org/10.1038/s41409-018-0245-y CORRESPONDENCE Peripheral flow-MRD status at the time of autologous stem cell collection predicts outcome in multiple myeloma Ivana Moor 1 ● Vera U. Bacher 2 ● Barbara Jeker 1 ● Behrouz Mansouri Taleghani 2 ● Beatrice U. Mueller 3 ● Peter Keller 4 ● Daniel Betticher 5 ● Thomas Egger 6 ● Urban Novak 1 ● Thomas Pabst 1 Received: 9 February 2018 / Revised: 6 May 2018 / Accepted: 8 May 2018 / Published online: 8 June 2018 © Macmillan Publishers Limited, part of Springer Nature 2018 Flow cytometric detection of minimal residual disease (flow- MRD) in the bone marrow is increasingly considered crucial for monitoring myeloma (MM) patients since it can add important information on outcome after therapy of patients who achieve a complete remission (CR) independently of the specific treatment compounds used [1, 2]. Advantages of such flow-MRD assessments comprise its relative simplicity, rapidly available results, and ubiquitous clinical applicability [1–3]. Potential major limitations involve the lack of stan- dardization of flow-MRD for MM patients and its decreased sensitivity compared to PCR-based approaches [2–6]. How- ever, the recently reported EuroFlow guidelines for next- generation flow cytometric (NGF) MRD monitoring of MM patients have established an increased sensitivity with a level of detection of 10 -6 [7]. This NGF approach demonstrated a very significant impact on PFS of MM patients, even among those MM patients in CR or even stringent (s)CR, thereby further improving the predictive clinical value of conventional flow-MRD. Although flow-MRD approaches summarized above relied on bone marrow material, other studies investigated the significance of the presence of clonal plasma cells in the peripheral blood at diagnosis of MM, before or after auto- logous stem cell transplantation (ASCT) [8, 9]. However, no information is available so far using flow-MRD from per- ipheral blood exactly at the day of collection of peripheral stem cells in MM patients planned to undergo first-line consolidation treatment with ASCT. Given the relevance of potential malignant plasma cell contamination of the auto- graft, we assessed the prognostic significance of circulating aberrant plasma cells by multiparameter flow cytometry from the peripheral blood at the day of stem cell collection. We studied 75 consecutive MM patients in first remission who received at least one melphalan-based high-dose che- motherapy (HDCT) with ASCT at the University Hospital of Bern, Switzerland, between 2010 and 2015. The majority— 80% of the patients—had received a bortezomib/dex- amethasone based induction treatment, and the clinical char- acteristics are summarized in Table 1. All patients have given written informed consent, and this study was approved by the local ethics committee of Bern, Switzerland. Peripheral blood was analyzed by multiparameter flow cytometry for CD34 + cells and for clonal plasma cells at the day of peripheral stem cell collection. Samples were investi- gated using the BD platform (BD FACSCanto II system) and Diva software. The following fluorochromes were used: CD45—APC-H7; CD38—APC; CD138—PerCP; CD19— PE-Cy7; CD56—V450; kappa—FITC; lambda—PE. Kappa and lambda were purchased from Dako/Agilent, all other antibodies were from BD Biosciences. The type of immu- noglobulin and involved light chains at diagnosis were known in all patients. The primary gating strategy included FSC, SSC, CD45, CD38, and CD138 properties within the same tube [9]. Aberrant phenotypic patterns were identified by analysis of CD38, CD19, CD45, CD56 expression, and intracytoplasmatic light chain expression [5, 10–13]. Patients with aberrant plasma cells above 10 -5 in the peripheral blood * Thomas Egger thomas.pabst@insel.ch 1 Department of Medical Oncology, Inselspital, University Hospital Bern, Bern, Switzerland 2 Department of Hematology, Inselspital, University Hospital Bern, Bern, Switzerland 3 Department of Biomedical Research, University of Bern, Bern, Switzerland 4 Department of Hematology, Regionalspital, Langenthal, Switzerland 5 Department of Oncology, Kantonsspital, Fribourg, Switzerland 6 Department of Oncology, Kantonsspital, Solothurn, Switzerland Electronic supplementary material The online version of this article (https://doi.org/10.1038/s41409-018-0245-y) contains supplementary material, which is available to authorized users. 1234567890();,: 1234567890();,: